The proposed study is an attempt to evaluate the responsiveness of the serotonergic system in premenstrual syndrome. We propose to evaluate peripheral hormonal concentrations in response to fenfluramine pharmacologic challenge during the luteal phase of the menstrual cycle in 10 patients w/ prospectively documented premenstrual syndrome and 10 controls. Fenfluramine or placebo will be administered to the subjects in a double blind randomized cross over fashion. Prolactin, Cortisol, Progesterone, & serotonin will be measured for 6 hrs after.